Roundabouts on Alberta Highways

Tamara Soltykevych, E.I.T. (Presenter), Alberta Transportation

Peter Mah, P.Eng, Alberta Transportation

Bill Kenny, P.Eng, Alberta Transportation

Paper prepared for presentation

at the Geometric Design – Present Challenges Session

of the 2014 Conference of the

Transportation Association of Canada

Montreal, Quebec

Abstract

Roundabouts have become commonplace in numerous locations across the globe; however, they are

relatively new in Alberta. Experience has shown marked improvements in safety and efficiency, and thus

roundabouts have become an ideal option over signalized intersections or other intersection

improvements. Additionally, their operation and maintenance costs are typically lower than for signalized

intersections. However, in Alberta, there are concerns that current roundabout construction costs are high

in comparison to alternate options. Numerous commercial loads, including oversize and overweight

(OSOW) vehicles, use Alberta’s highway corridors on a daily basis. The department’s intent is to

maintain a highway system that will have no blockages for high loads or oversized loads. Roundabouts

may present a bottleneck if OSOW loads are not considered. This problem can be addressed by

constructing wider approaches and/or using wide aprons; yet this comes at a cost for construction and

may adversely affect operations by regular traffic due to higher speed entries. Another strategy is to make

the centre island completely traversable with removable signs. However, situations such as these may

present higher costs than anticipated. The department has identified potential high cost factors, including:

traffic accommodation during construction, size of inner circle and overrun areas and the required amount

of concrete, design life, etc. There is a general consensus that the cost will decrease once roundabouts

become less unknown to contractors, as presently they are not accustomed to roundabout construction.

The department aims to determine best design practices for roundabouts with the most cost-effective

solution. For example, one good design practice is to build a roundabout that works for current volumes

plus a reasonable time period (i.e. 10 years), and then be prepared to add additional lanes if required.

Aside from saving cost, this practice is safer and allows drivers to adjust to a simpler roundabout. Cost-

sharing formulas have also been proposed to finance the roundabout. For the purposes of this paper, a

comparison of construction practice and resulting costs of existing roundabouts will be presented.

Information on roundabout practices in other jurisdictions, with a focus on the accommodation of OSOW

loads, will be obtained through comprehensive literature review and communication with professionals.

The main intent of this paper is to identify potential improvements to current roundabout design and

construction and to provide recommendations on the most efficient solution that maximizes safety while

being fiscally acceptable.

Table of Contents

1.0 Review of Roundabouts in Other Jurisdictions ................................................................................. 1

1.1 Literature Review .......................................................................................................................... 1

1.2 Correspondence ............................................................................................................................. 3

1.2.1 Summary of Correspondence ................................................................................................ 4

2.0 Existing Roundabouts within Alberta ............................................................................................... 4

2.1 General Information ...................................................................................................................... 4

2.1.1 Traffic Volumes .................................................................................................................... 5

2.1.2 Geometric Data ..................................................................................................................... 5

2.2 Location-Specific Information ...................................................................................................... 5

2.2.1 Roundabout at Junction of Hwy. 8 and Hwy.22 near Bragg Creek ...................................... 5

2.2.2 Roundabout at Junction of Hwy.744, 100 Street and 96 Avenue in Peace River ................. 7

2.2.3 Roundabout at Junction of Hwy. 20 and Hwy. 11A in Sylvan Lake .................................... 7

2.3.4 Roundabout at Junction Hwy. 6, Hwy. 507, and Hewetson Avenue in Pincher Creek ........ 8

2.3.5 Roundabout at Junction of Hwy. 55 and Hwy.892, west of Cold Lake ................................ 9

2.3.6 Roundabout at Junction of Hwy. 44 and Hwy. 633 near Villeneuve .................................. 10

3.0 Roundabout Costs ........................................................................................................................... 10

3.1 Cost of Existing Roundabouts..................................................................................................... 11

3.2 Financing the Roundabout .......................................................................................................... 12

3.2.1 Alberta’s Funding Practice .................................................................................................. 12

3.2.2 Funding in Other Jurisdictions ............................................................................................ 12

4.0 Discussion ....................................................................................................................................... 12

4.1 Advantages .................................................................................................................................. 13

4.2 Disadvantages ............................................................................................................................. 13

4.3 Recommendations / Cost-Reducing Strategies ........................................................................... 14

5.0 Conclusion ...................................................................................................................................... 15

References ................................................................................................................................................... 17

1

1.0 Review of Roundabouts in Other Jurisdictions

Roundabout designs and implementation of roundabouts in other jurisdictions have been investigated

both by literature review and through communication with design professionals.

1.1 Literature Review

Roundabouts have been proven to be feasible and advantageous at many locations. According to the

Transportation Research Board, a single lane roundabout is likely to operate effectively for intersection

daily entering volumes of 0-18,000, with a general rule of thumb that the sum of entering and circulating

volumes for each approach is less than 1,000 vehicles per hour. It has also been found that while initial

construction costs may be higher for a roundabout, the ongoing maintenance is less costly than for

signalized intersections. The three key considerations for horizontal design of a roundabout are design

speed, path alignment and design vehicle. The design speed is defined by the theoretical speed that

drivers could achieve if taking the fastest path through the roundabout without regard to lane line striping

according to predefined criteria for offset from the curb, etc. For single lane roundabouts, maximum

theoretical entry speeds of 20-25 mph (32-40 km/h) are recommended. [1]

A feasibility study should be completed on any intersection being considered for a potential roundabout

location. Contents of a roundabout feasibility study report may include: current status of traffic

operations and safety, a conceptual roundabout configuration, a demonstration that the proposed

configuration can be implemented feasibly and will provide adequate capacity, potential complicating

factors, evidence of community consultation, and an economic analysis. The first roundabout in any

geographic area requires an implementing agency to perform beyond regular due diligence. The full

range of design and analysis alternatives should be explored in consultation with other operating agencies

in the region. Designers must ensure that the roundabout accommodates the design vehicles, achieves

capacity, provides slow and consistent speeds and smooth channelization and is overall safe. If the

roundabout accommodates pedestrians then it must be designed to provide safe passage. The slope of the

truck apron should generally be no more than 2% as greater slopes may increase the likelihood of loss-of-

load or tipping incidents. Generally, it is not desirable to place roundabouts on steep grades. It is also

beneficial to stage the construction of a multilane roundabout to allow road users to become familiar with

a relatively simple roundabout before adding extra lanes or turning roadways that may be needed when

the volume increases. As future traffic volumes and patterns are difficult to predict, the need for a more

complex layout may never materialize. Generally, diverting or detouring as much traffic from the

intersection as possible is the most desirable option for efficient construction. [2]

A roundabout can offer operational improvements over other intersection types, such as higher capacity

and lower delays. In addition, roundabouts offer significant benefits for improving safety and can often

be justified solely on the basis of crash reductions and severity, particularly for reducing serious injury

and fatal crashes. Recent research of roundabouts in the United States identified crash reductions of

approximately 35.4% for all crashes and 75.8% for injury crashes when an intersection was converted

from a signal or stop control to a roundabout.[2]

However, roundabouts may come with a high capital cost.

Factors contributing to costs may include: maintaining traffic during construction, large amounts of

landscaping in the central and splitter islands, higher than typical pavement design life, extensive signage

and lighting, and the provision of curbs on all outside pavement edges.[2]

2

Public acceptance of roundabouts has often been found to be one of the biggest challenges facing a

jurisdiction that is planning to install its first roundabout. A public involvement process should be

initiated as soon as practical, preferably early in the planning stages of a project while other intersection

forms are also being considered. A successfully implemented roundabout, especially one that solves a

perceived problem, can be an important factor in gaining support for future roundabouts at locations that

could take advantage of the benefits that roundabouts may offer.[2]

Vertical ground clearance and curbs in particular are a major problem for large trucks and loads that are

oversize and/or overweight (OSOW) vehicles. Using a larger design vehicle such as a WB-67

(comparable to a WB-20 in Canada), particularly on state highways, would make it easier to

accommodate OSOW vehicles. It is possible to have a road through a roundabout for OSOW vehicles

with an offset entrance if the OSOW vehicle moves to the opposite lane prior to entering. National

Network Commercial Vehicle Size Standards in the United States regulate the length, width, height, and

weight of commercial vehicles traveling throughout the country. Some jurisdictions (e.g. European

countries) do not have issues with OSOW vehicles simply because they strictly regulate truck size;

however this is not desirable in Alberta (according to government policy) due to the necessity to facilitate

the various industries that wish to move large loads on the public provincial highway network. Truck

aprons should be designed so that they are traversable for trucks but discourage passenger vehicles from

using them. They should be of a different material than the traveled way. In the United Kingdom for

example, ‘grasscrete’ is used, which is a stabilized turf system that allows OSOW vehicles to travel

straight through the roundabout. Another option popular in some European countries is the use of low,

mountable cobblestone instead of concrete. However, these practices may not always be feasible in

Alberta as the turf or cobblestone could deteriorate quickly due to the volume of OSOW vehicles using

the roundabout. Another jurisdiction with a unique practice in accommodating OSOW vehicles is

Minnesota, where “superload corridors” accommodate sizes that reportedly cover 80% of OSOW

vehicles, and “expanded envelope corridors” can accommodate even larger and heavier permitted loads;

however, policy prohibits construction of roundabouts on these corridors.[3]

The British Columbia (B.C.) Ministry of Transportation (MoT) uses the 2003 Kansas Roundabout guide

as a primary resource. Their policy considers roundabouts as the first option for intersection designs

where four–way stop control or traffic signals are supported by traffic analysis. The design vehicle for

roundabouts is a WB-20 unless otherwise agreed upon by the Ministry.[4]

University of Texas and Kittleson & Associates state that during construction of a roundabout, it is best to

detour all legs. They also provide a possible staged construction sequence: Install signing and lighting,

construct widening, reconstruct or resurface approaches, construct splitter islands, delineate the central

island and construct the central island.[5]

The Florida Department of Transportation (DoT) requires a formal “justification report” to document the

selection of a roundabout as the most appropriate traffic control mode at any intersection on their State

highway system. Conversely, the Maryland Department of Transportation requires consideration of a

roundabout as an alternative at all intersections proposed for signalization.[6]

3

In 2000, state-built roundabouts on state highways in the Unites States ranged in cost from $350,000 -

$500,000. There are many appropriate locations for roundabouts, such as high accident locations,

locations with high delays, four-way stop intersections, etc. Common reasons behind the success of

roundabouts include high capacity and fluidity, safety, shorter delays and reduced environmental impacts,

and aesthetics and urban design. However, some problems have also been encountered; these include

delays to high-volume approaches in the case of unequal control volumes, lack of clear right-of-way

control for pedestrians, maintenance, and complicated and costly construction. Some methods identified

by the Maryland DoT to reduce costs of the roundabouts include: detouring traffic during construction,

limiting resurfacing to the roundabout, simplistic landscaping, reducing size of signs, and the possibility

of area-wide contractors to bid on larger quantities.[7]

1.2 Correspondence

According to a representative from the Connecticut DoT, if a roundabout cannot accommodate an OSOW

vehicle then the OSOW vehicle is directed to an alternate route; however, this has not yet been an issue

that they are aware of. Their biggest issue to date is low-boy truck trailers due to their limited vertical

clearance. In general, they have found that if the truck apron has the same cross-slope as the circulatory

roadway, the extra height (usually 1-2 in. (2.5-5 cm)) does not cause a problem. For a very large load,

they would most likely shut down all approaches and then allow the truck through, using the other side if

necessary. They recommended building a roundabout based on current volumes, possibly with some

growth, and leaving room for expansion to whatever future design year is being considered. They stated

that aside from saving cost, this practice also helps maximize safety and allows drivers to get used to a

simpler roundabout before getting into multiple lanes.

A representative with the B.C. MoT mentioned that the ministry has a policy to consider roundabouts as

the first option for intersection designs where a degree of traffic control greater than a two-way stop is

required. Roundabouts are considered on all roads including corridors of speed 70 km/h and higher. They

stated that 25 roundabouts have been completed within B.C., and an additional 10 roundabouts are

currently under review. According to the spokesperson, the design requirements for all B.C. highways

including intersections and roundabouts is premised on meeting the legal vehicle size of a tractor trailer

truck classified by the Transportation Association of Canada (TAC) as a WB-20. The total paved

circulatory width should, at a minimum, accommodate the largest frequent design vehicle, which is

typically a WB-20 side by side with a passenger car. In addition, the highway legs through the

roundabout shall be a minimum of two lanes per direction where these lanes may be any combination of

left, through and right turn lanes. There has been a case where the Ministry has modified the design of a

roundabout on corridors being used to move loads as wide as 7.32 m on a fairly regular basis. Since these

loads essentially cover the surface area of a two-lane highway they can only be moved at night. In this

circumstance the redesign did not impact the central part of the roundabout; rather, it involved raised

channelization on the approaches.

A spokesperson with Washington State Department of Transportation (WSDoT) stated that in 2006,

WSDoT and the Washington Trucking Association (WTA) created a significantly different “curb detail”

(friendly towards sidewalls of tires) and also made a commitment to install removable signs (where the

base is detachable, but still crashworthy and stable in wind) in order to make sure that there are numerous

ways to deal with the arrival of OSOW vehicles. In addition, WSDoT altered the height of truck aprons

to 3” (7.6 cm) and are considering lowering it further to 2” (2.5 cm) based on their experiments.

4

1.2.1 Summary of Correspondence

A good design practice is to build a roundabout that works for current volumes plus a reasonable time

period (i.e. 10 years), and be prepared to add additional lanes in the future.

Traffic control/accommodation is a high cost factor.

A big issue is designing to accommodate low-boy vehicles due to their limited vertical clearance.

Therefore, the apron slope should be similar to that of the circulatory road.

For a very large load, it may be possible to shut down the roundabout completely, using the wrong

way (counter flow) if necessary.

One jurisdiction has made a commitment to install removable signs and have a curb supportive of

sidewalls of tires to accommodate OSOW vehicles.

Research of vehicle type and how often it will use the intersection is crucial to design.

Public input process may be lengthy but is worthwhile.

The general consensus is that roundabouts are much safer than signalized intersections.

2.0 Existing Roundabouts within Alberta

2.1 General Information

The department currently provides Design Bulletin 68 as its standard for roundabout design in the

province. [9]

To date, seven roundabouts have been constructed on the provincial highway network. They

are located as follows and are listed in the order in which they were constructed:

1. Highway 63:12 Interchange in Fort McMurray (King Street and Tolen Drive)

2. Junction of Highway 22 and Highway 8, northeast of the Hamlet of Bragg Creek

3. Junction of Highway 744, 100 Street and 96 Avenue in the Town of Peace River

4. Junction of Highway 20 and Highway 11A in the Town of Sylvan Lake

5. Junction of Highway 6, Highway 507 and Hewetson Avenue in the Town of Pincher Creek

6. Junction of Highway 55 and Highway 892, west of the City of Cold Lake

7. Junction of Highways 44 and 633 near Villeneuve (opened to traffic in December 2013)

There has been another roundabout constructed at Leva Avenue and Lantern Street in Gasoline Alley,

Red Deer County, which opened to the public in August 2013. It was designed and reviewed by Red Deer

County. The Government of Alberta provided partial funding to the County of Red Deer for the Leva

Avenue improvement project; this funding was used for linking Leva Avenue to an existing range road.

Alberta Transportation has also constructed a roundabout along Valley Ridge Boulevard, north of the

Trans-Canada Highway 1 crossing through Calgary as 16th Avenue. This roundabout is within the City of

Calgary’s jurisdiction.

5

In addition to communicating with various experts across the country and in the United States, Alberta

Transportation personnel have been approached to solicit their opinions on the implementation of

roundabouts within the province. All of the feedback is included in the respective roundabout section

with the exception of the following: one general opinion was provided by a representative for the Central

Region. He mentioned that the high cost of roundabouts is linked to the fact that they are quite new to the

province, and believes that the cost will decrease once they become more commonplace and less of an

unknown entity for contractors. In addition, he stated that more consideration should be given to the

frequency of OSOW loads that would utilize the roundabout; he is of the opinion that some roundabouts

are overdesigned in terms of structural thickness, which implies that the cost of concrete and surfacing

materials for the project is higher than necessary.

2.1.1 Traffic Volumes

Turning Movement Diagrams (TMD’s) provide information regarding the types of vehicles that utilize a

particular intersection. The available highest and lowest average daily traffic volumes for Bragg Creek,

Cold Lake, Pincher Creek, Sylvan Lake and Villeneuve roundabouts for the past decade are summarized

in Table I, located at the end of the report.

2.1.2 Geometric Data

Geometric data for the existing roundabouts was gathered and compiled for easy comparison. The data is

presented in Table II. Notable observations on the data are as follows:

None of the roundabouts were designed by the same consultant, with the exception of Fort McMurray

interchange and Bragg Creek.

Cold Lake has a significantly wider apron than the rest.

Bragg Creek has the largest inscribed circle diameter and central island diameter.

Cold Lake and Bragg Creek roundabouts are higher speed roundabouts because they are located in a

rural setting, whereas Sylvan Lake, Peace River, and Pincher Creek roundabouts are designed for

lower speed because they are located in an urban setting.

All roundabouts have four legs, with the exception of Peace River which has five legs.

2.2 Location-Specific Information

2.2.1 Roundabout at Junction of Hwy. 8 and Hwy.22 near Bragg Creek

A design report completed by the consultant (EarthTech Canada Inc.) contained information on planning,

the results of which are summarized below.

Average Annual Daily Traffic volumes (at time of design) were: 8300 at north leg, 7000 at south leg,

6900 at east leg, and very low volume on west leg.

The intersection was analyzed for the 2023 traffic horizon – multi-way (four-way) stop control vs.

signalized intersection vs. roundabout.

Two alternatives were forecasted to be effective: a signalized intersection with a north/south left turn

and a roundabout with single lane approaches on all legs.

6

Preliminary cost estimate of the roundabout was almost half of that of signalization.

It was sized to accommodate off-tracking of large trucks up to WB-36 sized vehicles and to include

the future option of a second lane on the “circle.”

Construction on the roundabout commenced on July 19, 2007. A Northbound (NB) / Southbound (SB)

detour for Hwy 22 was constructed and opened along the west side of Hwy 22. New lanes and the circle

were open to traffic on November 1, 2007. The project was completed and construction was shut down on

August 18, 2008. Some problems encountered during construction included the following:

Many rain days hampered progress.

There were a few minor deficiencies for pavement segregation and smoothness.

When the roundabout opened there was initial public confusion, but they soon adjusted.

General opinion after the roundabout was opened is that it effectively dealt with the volume and type

of traffic at this intersection.

Paving in the roundabout proved to be quite challenging especially when doing the final lift with

traffic following through and so production was limited.

There were some discrepancies with contractor and traffic accommodation, including not using

standard retro-reflective signs, using non-standard barriers and small, flimsy, portable sign stands.

There were some suggestions that the diameter of the circle should have been smaller, as the diameter

is in the upper range for modern roundabouts.

The roundabout approaches required reconstruction in a curvilinear fashion to provide for traffic

calming (slowing) and proper entry geometry.

Meanders in the approaches conflicted directly with overhead power on one side, requiring pole line

relocation which in turn affected grade construction.

The contractor asserted that the timing of the removal of the power utility was the largest single

impact on the project completion.

Input from the Program Management Branch included the following: While the consultant has

underestimated the project cost, the difference is more likely related to the very heavily committed state

of the industry and tight construction timelines. It is not particularly desirable work as it is low

production piecemeal at numerous locations and with the volume of work available the contractors have

the luxury of setting their own prices. While the tender price for this project is very high, three bids were

received with the second bidder being only $100,000 higher than the low bid. It is unlikely that re-

tendering would provide any lower prices. This project provides major safety improvements; because of

the importance of the work and available funding, the Region recommends awarding to the low bidder.

The consultant’s opinion of the contributing factors affecting the increase in cost included:

The Alberta economy pushes construction price up at a fast pace.

Most contractors are at or near capacity to have projects finished within this season.

A June tender schedule for this October completion date requires bidders to reschedule their already

tight availability, which resulted in a premium price deferential.

Small, slow production jobs were tagged on to this project, and bidders put in a higher than normal

mobilization to allow for a minimum of mobilizing three times.

Traffic accommodation is not a separate bid item. All works are intersection treatments therefore

bidders anticipated full traffic accommodation setup at each of the 5 locations (instead of the normal

one or two construction zone setups on lineal projects).

Specific bid items of significant variance include: mobilization, common excavation, Granular Base

Course (GBC), Asphalt Concrete Pavement (ACP), and concrete surfacing.

7

2.2.2 Roundabout at Junction of Hwy.744, 100 Street and 96 Avenue in Peace River

Details obtained from the contract package for the Peace River roundabout are outlined below.

Major work on the project was delayed by three major causes: extension of the contaminated waste

reclamation, re-design of the roundabout due to the installation of the retaining wall, and inclement

weather conditions.

The extension of the roundabout into the main street delayed the project for 15 days.

The re-design of the roundabout due to the installation of the retaining wall delayed the project for

approximately 18 days.

As per AT’s instructions to open the roundabout with concrete medians, the contractor completed

work during inclement weather conditions. Specifically, the contractor was delayed or unable to

complete work days from October 31, 2009 to November 12, 2009 when the roundabout was due to

be opened for the winter.

The AT project administrator who worked on the roundabout in Peace River mentioned that this

particular roundabout was completed over two construction seasons, with winter concreting (with heating

and hoarding). In addition, a unique feature of this roundabout is that it has semi-mountable curbs inside

a concrete apron, with brick work inside the semi-mountable curb in the centre. He mentioned that it has

the same effect but looks different from other roundabouts and therefore has raised some questions.

Overall, he has observed that the roundabout has been a huge improvement in this location as the

difference in user costs outweighed the difference in construction costs.

2.2.3 Roundabout at Junction of Hwy. 20 and Hwy. 11A in Sylvan Lake

A summary report completed by the consultant (Al-Terra Engineering) on the Sylvan Lake roundabout

was reviewed and is summarized below.

Construction included base work, paving, pouring curb and gutter, pouring medians, and upgrading

lighting, occurring for around four months.

After grade widening was complete in each quadrant, it was either graded or paved to tie into the

existing pavement so that traffic could partially move over onto the new surface to allow construction

to start in the original travel lanes.

Some base and grading work was completed concurrently in two separate quadrants to minimize site

occupancy.

Most utility adjustments were carried out in 2007, before construction started; this was a great benefit

to the project since the construction site was small.

Some problems encountered during construction involved the following:

Scheduling was difficult due to the piecemeal nature of the project.

Building alignment was tedious since part of each quadrant encroached into the existing travel lanes

while the other part involved widening the existing grade.

Heavy rains and construction scheduling to constantly accommodate traffic delayed progress.

Due to the wet ground conditions, the Contractor was instructed to place a geotextile under all

granular material.

8

The modified construction price came in at 3.2% above the modified tender price. Traffic accommodation

increased costs; the contractor stated that future intersection construction of this type would benefit from

a full intersection closure and major detours which would significantly decrease costs and site occupancy.

Areas of unexpected high costs included: common excavation, borrow excavation, GBC and ACP.

In conclusion, the consultant mentioned that future rural roundabouts will benefit from good design,

consideration of urban design standards as to how they can apply to low speed roundabouts, efficient

coordination of sub-contractors, and continued emphasis on safety and proper traffic accommodation.

An AT construction engineer who was involved in the Sylvan Lake roundabout pointed out a few things

unique to it that should be taken into consideration when examining costs. Firstly, the final pave for the

roundabout occurred approximately three years after the initial construction to reduce traffic delays, save

on costs due to scale of quantity, and because it also fit in better with the curb and gutter at time of

construction rather than trying to match it later. In contrast, the final pave is being done at time of

construction on current roundabout projects. In addition, there were minimal right of way requirements

for the roundabout. Finally, the Sylvan Lake roundabout design did not consider OSOW vehicles.

2.3.4 Roundabout at Junction Hwy. 6, Hwy. 507, and Hewetson Avenue in Pincher Creek

An AT Engineer who was involved in the Pincher Creek roundabout mentioned that the roundabout was

not triggered by any Traffic Impact Assessment (TIA); rather, a series of developments in the area led to

concerns voiced by the Town of Pincher Creek that the existing intersection was unsafe, needed upgrades

(preferably signalization) and pointed to a number of TIA’s and studies by the Town. The engineer

believes that these studies were unrealistic as they were based on high estimates of growth/development

without any calibration with field data or analysis of growth rate/demographics. He stated that this is

typical of most TIA’s and therefore they are not a good basis for programming capital projects.

Construction commenced on July 19, 2011 and was completed on September 22, 2011. The successful

bidder was 6.2% above the design estimate. Cost overrun from estimated to actual construction quantities

were as follows:

Channel excavation, common excavation, granular fill, hand-laid riprap and erosion control soil

covering underran, removal of existing painted lines and extra work for ditch regrading was not

required as estimated.

GBC overran due to more overbuilding than expected.

Extra work included: filter fabric for widening and rock check dams, culvert extension, enlarged

breakaway bases, and steel post base and breakaway assembly.

The contractor was awarded a bonus for density, gradation, segregation, traffic signing compliance,

and site occupancy.

According to the consultant (ISL Engineering and Land Services), the operation was well organized and

productivity was high. The consultant concluded that stakeholders were satisfied with the final product

and the overall project was considered satisfactory.

9

2.3.5 Roundabout at Junction of Hwy. 55 and Hwy.892, west of Cold Lake

The consultant on the Cold Lake roundabout, Clifton Associates, confirmed that the cost of construction

was approximately four times the amount of a signalization system. However, to provide signalization

additional Right-of-Way (ROW) would have been required, as well as widening at the approaches to

provide right turn lanes and general intersection improvement. The consultant mentioned that

construction of this type of roundabout, where the legs meet the roundabout at a tangent, requires a

substantial amount of civil works to be carried out to “offset” the legs in the lead up to where they join the

roundabout. Less civil works are required when the approach legs are “perpendicular” to the

circumference of the roundabout; road users in this type of roundabout have to slow down otherwise they

will collide with the roundabout structure.

Significant traffic accommodation occurred to properly operate the detour and to ensure the work zone

was free of vehicles. Local issues included heavy traffic using minor roads as short cuts which caused

disturbance to the residents. However, there were very few public complaints. The consultant also

mentioned that OSOW loads had been permitted to use Highway 55, approaching the roundabout from

the west and exiting heading north on Highway 892 as these two highway sections are part of the high

load corridor. Modifications were recommended and all OSOW vehicles that arrived at the construction

site were sufficiently accommodated.

According to the consultant, the construction process was slow, although in the consultant’s opinion that

was more of a reflection on the contractor’s inexperience with this type of construction than was due to

the roundabout or its design. There were no major problems that occurred during construction. Some

minor issues encountered were as follows:

The design did not deal with all surface water and two swales had to be incorporated.

The design had “free end” extruded curbing with nothing to back them so if it was mounted by a large

vehicle the curb would fail.

The design was originally not for a 50 year life-span so the pavement had to be redesigned after the

project had started to ensure compliance.

The method for holding up sign posts was not well defined in the documents and as a result led to

misunderstandings by the contractor.

In closing, the consultant stated that the roundabout has been excellent at managing the flow of traffic

over time and believes roundabouts will prove to be a great success as more people become accustomed

with their use.

10

2.3.6 Roundabout at Junction of Hwy. 44 and Hwy. 633 near Villeneuve

The roundabout at the intersection of Highways 44 and 633 has recently (Nov/Dec 2013) opened to the

public. The consultant, CIMA+, shared some knowledge based on their experience. Firstly, the item with

the largest implication on costs was the requirement for accommodating OSOW vehicles. The design

vehicles accommodated were a Heavy Hauler (Low Boy) Vehicle (46.8 m), a Platform Trailer Vehicle

(54.3 m) and a Superload-Reactor Vehicle (97.8 m), all of which have very large tracking paths. This

caused the roundabout footprint to be considerably larger than if the design vehicle was a WB-36. As a

result, there were requirements for a greater paved surface area, additional curb and gutter and more

ROW. Highway 44 is designated as a Long Combination Vehicle (LCV) corridor. The need to

accommodate OSOW vehicles was mandated as part of Design Bulletin 68 [9]

. In the consultant’s design

they assumed that OSOW vehicles would travel counter flow on the approach to the roundabout

circulatory roadway and cross over the splitter islands. While this reduced the overall footprint, it also

resulted in the need for semi-mountable curbs throughout the roundabout along with making any sign

within the splitter islands removable.

In addition, the consultant mentioned that the perpetual pavement design utilized at the roundabout also

led to increased projected costs. This design, which has a nominal design life of 50 years, consists of

170–300 mm ACP over 400-600 mm GBC which is significantly thicker than a pavement with a more

typical 20 year pavement design life. The rationale behind using the perpetual design is that there is less

risk of overlaying the curb and gutter in the future. A second option would be to use a more traditional 20

year design life, with the risk that selective reconstruction of the surfacing within the roundabout may be

required at rehabilitation. In the consultant’s past experience with City of Edmonton, a 20 year pavement

design life is typically utilized on all roadways, most of which have an urban style cross-section. Another

option would be to utilize a 20 year design life but to increase the rehabilitation cycles (i.e. 10 years),

which would repair any distresses before they permanently affect the pavement structure. Finally, the

consultant stated that some additional guidance may be necessary in determining more realistic unit

pricing. For example, a specific mark-up on unit pricing to consider a roundabout scenario may be

beneficial.

3.0 Roundabout Costs

Factors to consider with roundabout costs include, but are not limited to, the following:

Traffic Accommodation: Cost of maintaining traffic during construction may be relatively high for

retrofitting roundabouts. It can be very costly to accommodate traffic if an entire new detour is

constructed. Many individuals have mentioned that traffic accommodation is one of the biggest

factors contributing to the overall cost in roundabout construction.

ROW Acquisition: ROW costs are normally not a significant additional cost, but are worth

considering as roundabouts typically take up more space than conventional intersections. With the

exception of the Pincher Creek roundabout, which fit into the existing intersection, the cost of

acquiring ROW for the other existing AT roundabouts ranged from $81,000 - $380,000 (3.8-4.8% of

bidding price).

Diameter and Overrun Areas: The diameter of the roundabout has a direct influence on cost as

increased size leads to higher quantities of materials required. Both the diameter and overrun areas

should be designed as modestly as possible to accommodate the maximum capacity without

compromising safety.

11

Surfacing: Based on the data collected on the existing roundabouts, the amount of GBC and ACP

utilized in construction has a direct correlation with the overall cost. Additionally, the relative

locations of the roundabouts within the province may increase hauling costs. Directly related to the

amount of ACP required is the roundabout design life. Personnel involved in previous roundabout

projects have stated that more consideration should be given to the frequency of OSOW loads that

would utilize the roundabout as some roundabouts are overdesigned, which implies that the cost of

pavement is more excessive than necessary. More study is required in surfacing strategies to find

ways to reduce the quantity required, as surfacing can become very expensive with increasing

pavement thickness. Currently pavements for roundabouts are designed for 50 years. Two suggestions

are made based on observations of practices elsewhere: 1) use a 10 or 20 year design period for the

travel lanes and be aware that resurfacing may be needed in the shorter term due to the need to re-

allocate lane usage (with fresh pavement markings and lines) and 2) reduce the pavement thickness

on the over-run areas and central apron as the loading on these areas is very infrequent. Pavement

designers should visit some existing roundabouts to get a better understanding of the very low usage

of all areas that are off the main travel lanes.

Accommodating OSOW vehicles: Designing the roundabout to accommodate OSOW vehicles will

certainly lead to increased costs over a roundabout that does not have to accommodate any OSOW

vehicles. Indeed, in AT’s newest roundabout at the junction of Highway 44 and Highway 633

(Villeneuve), the consultant confirmed that the item with the largest implication on cost was the

requirement of accommodating OSOW vehicles.

Contractors / Tendering Schedule: If a project is tendered later in the year, the price will increase as

the contractor has less time to complete the project. At the Bragg Creek roundabout, a June tender

schedule for an October completion date required bidders to reschedule their already tight availability

resulting at a premium price deferential. There were not many contractors available to bid on the

project for completion in the same year. Many are of the opinion that one highly likely source of high

cost is linked to the fact that roundabouts are quite new to the province; this cost will decrease once

they become more commonplace and less of an unknown for contractors.

3.1 Cost of Existing Roundabouts

The total cost of each existing roundabout is summarized along with its geometric data in Table II, which

can be viewed at the end of the report. The bid items used in construction which have had the most

significant impact on cost are summarized below:

Common excavation and concrete curb cost significantly more in the Bragg Creek and Villeneuve

roundabouts.

The quantity of asphalt concrete pavement used increases concurrently with total cost.

GBC surpassed $1.2 million in the Villeneuve roundabout.

Concrete sidewalk cost significantly more at Sylvan Lake than at other locations.

Site occupancy cost was significantly higher at Cold Lake and Villeneuve locations.

Mobilization cost surpassed $1.2 million at the Bragg Creek roundabout. However, the mobilization

for only the roundabout was lumped together with the mobilization for other intersectional

improvements.

Granular fill cost significantly more at Cold Lake than at the other locations.

Borrow and subgrade excavation was quite costly at Villeneuve, and either very low or non-existent

at all other locations.

12

3.2 Financing the Roundabout

3.2.1 Alberta’s Funding Practice

The current policy requires that developers be responsible for upgrades to highway intersections. At

times, this policy may conflict with the department’s business goal of connecting communities and

supporting economic and social growth. A single development with a private means of access to the

highway is to be responsible for all costs for highway improvements attributed to their developments.

The current policy allows for department funding for developments accessing the highway if there is a

highway construction project at that location identified in the department’s three year business plan. The

current recommendation is that upon receipt of development applications where highway improvements

are anticipated, a TIA should be requested to identify what improvements, if any, are required for existing

traffic, and what improvements are required to accommodate the development.

3.2.2 Funding in Other Jurisdictions

With respect to the idea of cost-sharing, a spokesperson from Connecticut DoT states that this is not an

issue for the Connecticut DoT as all of their roundabouts are completely federally funded, with the

exception of decorative features such as illumination posts and signage.

A representative from B.C. MoT has identified that the British Columbia MoT has a cost-sharing

agreement with the Insurance Corporation of B.C. (ICBC) for safety projects. This is a $3-5 million per

year partnership and the ICBC project funding is based on their investment criteria which are dependent

on safety performance of the location. Since roundabouts are considered a safer form of traffic control

they qualify for ICBC funding. Typically, the cost-sharing agreement with ICBC is for ministry driven

projects and not development driven. Thus, the developer will have to fund the intersection

improvements that are triggered by the development.

According to a spokesperson from WSDoT, cost-sharing is very site-specific and precise to the

stakeholders involved who share jurisdiction or who can benefit from the “more efficient/safer”

intersection. If a development comes forward that requires mitigation (there is a threshold for the number

of trips it will add to the roadway), then the development is responsible for funding the improvement, per

the WSDOT standards for a roundabout design or other fix. In the past the traditional solution has been

left or right turn channelization or a signal; however roundabouts are increasingly becoming the preferred

choice of improvement or resolution. If a development is proposed for an area that is already funded, for

example at an intersection, costs can be shared with the development and potentially get quicker approval.

4.0 Discussion

There are many advantages and disadvantages to the modern roundabout. These factors are taken into

consideration during highway planning and assist in the decision of whether the implementation of a

roundabout is warranted.

13

4.1 Advantages

Less Serious Collisions: Head-on and angle collisions are virtually non-existent because of the

circular rather than opposing flow of traffic. In fact, roundabouts in the USA and other countries

have achieved a 50-90% reduction in collisions compared to intersections using two or four-way stop

control or traffic signals.[8]

Low Operation and Maintenance Costs: The only maintenance costs for a roundabout are for

landscape maintenance and occasional sign replacement. Even if the construction cost of a

roundabout is higher than for traffic signals, an economic analysis including construction, operation,

maintenance and collision cost reduction associated with each type of control will usually show that a

roundabout has a higher benefit/cost ratio than a signalized intersection.

Self-Regulating: Generally, a well-designed roundabout closely matching approach and mid-block

capacity rarely needs altering, except where the road is widened and the number of approach lanes is

increased.

Environmental Benefits: Roundabouts account for a reduction in noise levels, and can be expected to

result in a lower pollutant output as the result of reduced delay and fewer vehicle stops and starts.

Traffic Calming: Roundabouts can accommodate traffic at locations where there is a need for traffic

calming, such as at the boundary between rural and urban environments.

Operational Improvement: A roundabout will always provide a higher capacity and lower delays than

All-Way Stop Control (AWSC) operating with the same traffic volumes and right-of-way limitations.

A single-lane roundabout may be assumed to operate within its capacity at any intersection that does

not exceed the peak-hour volume warrant for signals. Roundabouts are also associated with better

utilization of connected roads and greater capacity. During a power outage, roundabouts will continue

to allow traffic movement.

4.2 Disadvantages

Heavy Flows vs. Minor Flows: In the case of unequal approach volumes, the modern roundabout

gives the advantage to the minor flow, adding delay to the heavy flow. This can be addressed by

metering of certain approaches when queuing occurs on the heavier traffic legs.

Pedestrian and Bicycle Right-of-Way: Additional assessment is warranted prior to constructing

roundabouts in areas where heavy pedestrian or bicycle activity is expected. Pedestrian and bicycle

flows can be an issue, depending on the volume. However, this is more of an issue for multi-lane

roundabouts.

Snow removal: Snow clearing may become an issue with modern roundabouts in winter conditions.

Although some have the advantage of allowing snow removal vehicles to turn around in the modern

roundabout, the added pavement that requires clearing can increase time for snow removal.

Raised Splitter Islands: In single-lane roundabouts, splitter islands limit circulation flexibility during

construction and in cases of collisions. This can be addressed by using mountable curbs.

Construction: Construction becomes more costly and complicated because of the need to grade a

larger surface and the maintenance of traffic during construction.

Topography: Roundabouts should only be considered in areas that can accommodate an acceptable

inscribed diameter and other appropriate geometric design elements. To provide adequate sight

distance for approaching drivers to perceive the intersection layout, it is good to locate the roundabout

either on level terrain or at the bottom of a sag vertical curve. Sight distance demands are minimized

through the use of low operating speeds.

14

Modelling and Simulation: The theory of gap-acceptance leads to complex assumptions regarding

driver behaviour. Sophisticated modelling is required to properly simulate reasonable traffic patterns.

An acceptable alternative is to use empirical models which are founded on decades of experience and

should be calibrated for the local driver experience level.

Public Acceptance: Often one of the biggest challenges facing a jurisdiction that is planning to install

its first roundabout is public acceptance, as the public may initially be wary where it is a new

practice. A successfully implemented roundabout, especially one that solves a perceived problem,

can be an important factor in gaining support for future roundabouts at locations that could take

advantage of the benefits that roundabouts may offer. As they can be a highly effective intersection

control method, it is a good idea for agencies to celebrate their successes if they would like

roundabouts to be more fully adopted in a timely manner.

4.3 Recommendations / Cost-Reducing Strategies

Recommendations on methods of reducing capital cost for the construction of roundabouts are provided

below.

Low Speed Environment: The design speed for a roundabout should be chosen with consideration of

the setting, i.e. rural or urban. However, it is more desirable to provide a low-speed environment as

curves can be tighter, leading to a smaller overall size and correspondingly lower cost.

Central Island: The central island could be traversable with the use of removable, crashworthy objects

in centre. All signs can be removed by escorts accompanying any OSOW vehicles. In addition, the

central island could have a strong base. The apron can be made less thick than previously constructed

roundabouts if the amount of OSOW vehicles is sufficiently less.

Surfacing: Currently the pavements in roundabouts are designed for 50 years, which certainly

contributes to the overall cost as they must be of a much stronger quality than if for a shorter life (e.g.

10 years). Other jurisdictions have found success in designing for a 10 year horizon, and ensuring

that there is the possibility to add on another lane if necessary. This is good practice as future traffic

predictions may never materialize. In addition, instead of adding resurfacing beyond the limits of the

project, the department could limit the resurfacing to that which is actually needed for the roundabout.

Reduce Diameter: In general, a smaller diameter will lead to a safer roundabout. Safety advantages

of a roundabout may begin to diminish when the diameter of the inscribed circle exceeds 75 m [8]

;

none of the existing roundabouts in Alberta exceed 75 metres. If the roundabout is single-lane, the

diameter could be reduced while the apron width could be increased correspondingly. In the case of a

multi-lane roundabout, the diameter may be reduced after careful consideration to the type of

roundabout (i.e. Case I, Case II, and Case III as per Design Bulletin #68) and accommodation for

OSOW vehicle movement.

Apron and Curbs: The apron should have a cross-slope of 2%, or whatever is required to

accommodate low-boy and OSOW vehicles. The height of the curb should be minimized to the best

extent possible to save on cost of concrete. Another option is to use rumble strips or other forms of

textured pavement, which would be at the same height as the road but would still deter drivers from

using the apron. This would also ease maintenance concerns.

Cost-Sharing: It is unlikely that developers will agree to pay for a roundabout if the estimated cost is

significantly higher than for a signalized intersection. Therefore, an option to this would be to have

developers cover the cost of a conventional intersection, and the government would cover the

incremental cost remaining for the roundabout. It is anticipated that once roundabouts become more

familiar to contractors the cost will decrease.

15

Analysis: Review of the amount of trucks actually using the apron of existing roundabouts would be

useful to ascertain whether the surfacing is overdesigned. This data can be used to improve future

design. There have been concerns raised by personnel involved in previous roundabout design that an

inadequate or inconsistent amount of analysis is completed before a roundabout is selected. Another

option would be to undertake smaller (lower cost) construction of roundabouts in two of the future

highway locations; one urban, one rural. The two roundabouts would be built and their operation

monitored. If they prove satisfactory, future designs could be based on a smaller prototype.

Design Exception: Allow design exception if there is an alternate route (as accommodation of large

vehicles is very costly or otherwise constrained).

Detours: During detailed design, constructability should be considered.

Design Vehicle and Accommodating OSOW vehicles: If a roundabout is designed to accommodate

OSOW vehicles or LCV’s, it will be more costly to construct. In some jurisdictions there are separate

corridors for OSOW vehicles to travel through, and thus they do not have to be accommodated at that

particular jurisdiction’s roundabouts. Overall this would increase efficiency of flow through the

roundabout and would decrease material required at the roundabout. Although it contradicts current

policy in Alberta, one option to consider would be to not construct any roundabouts on OSOW

vehicle corridors. In some cases OSOW vehicles and LCV’s cannot travel on particular corridors as

they cannot fit due to structures in the way. In these situations an alternate route must be provided.

Careful analysis of current LCV and OSOW vehicle routes should be completed to potentially reduce

the amount of corridors that must accommodate OSOW vehicles and LCV’s.

5.0 Conclusion

Alberta Transportation’s existing roundabouts have been described, and the construction process of each

one analyzed. A literature review of practices in other jurisdictions and correspondence with roundabout

professionals has been completed. A comparison of each of AT’s roundabouts has been provided and

high bid items have been identified. Roundabouts remain a relatively new concept in Alberta, and some

challenges have arisen in design and construction. These challenges have resulted in construction costs

higher than anticipated.

Benefits of roundabouts generally include reduced crash rates and severity, as well as reduced delay,

stops, fuel consumption, and emissions. Disadvantages may include higher maintenance costs,

complicated construction, and possibly increased delay in the case of extremely disproportionate

approach volumes. Costs associated with roundabouts may include construction costs, engineering and

design fees, land acquisition, and maintenance costs. Common challenges facing agencies that are

planning to install roundabouts include limited public acceptance and designing to accommodate OSOW.

A roundabout designed to accommodate significantly more loads than actually present will undoubtedly

lead to higher costs. Conversely, a roundabout designed for fewer loads than are actually present will

lead to safety concerns and quick deterioration of pavement. Therefore, it is evident that research into

traffic patterns and wheel paths is crucial to an efficiently designed roundabout. From observing the

construction process of each roundabout, it is also apparent that the efficiency of construction has a direct

correlation to cost.

16

Good design practice is to build a roundabout that works for current volumes plus a reasonable time

period (i.e. 10 years), and then be prepared to add additional lanes in the future. Aside from deferring

cost, this practice also helps maximize safety and allows drivers to get used to a simpler roundabout

before multi-lane roundabouts are introduced. It may be concluded that overall cost will decrease once

more roundabouts are built in the province and become more familiar to contractors who will then feel

comfortable lowering their prices. The public acceptance process will also become easier as people

become more accustomed to using a roundabout and are able to see the benefits that roundabouts provide

for themselves. General opinion is in favour of roundabouts; that although the capital cost may be higher,

the positive impact they have on society is worthwhile as roundabouts greatly improve safety and

decrease congestion, noise and pollution. Many jurisdictions are of the opinion that the overall benefits

associated with roundabouts, especially those of increased safety, are great enough that roundabouts

should be considered at all intersections.

17

References

1United States Department of Transportation. (2010). Roundabouts: An Informational Guide, Second

Edition. Washington, D.C.: Transportation Research Board

2United States Department of Transportation. (2010). Roundabouts - A Technical Summary. Federal

Highway Administration.

3Russell, E. et al. (2013). Accommodating Oversize/Overweight (OSOW) Vehicles at Roundabouts.

Manhattan: Kansas Department of Transportation.

4 Transportation, B. C. (2007). 740_Roundabouts, Supplement to TAC Geometric Design Guide. BC

MoT.

5 The University of Texas at Austin and Kittleson & Associates, Inc. (2011). Roundabout Evaluation and

Design Workshop. The Center for Transportation Research.

6 United States Department of Transportation. (2000). Roundabouts: An Informational Guide. Mclean,

Virginia: Federal Highway Administration.

7 Jacquemart, G. (1998). Modern Roundabout Practice in the United States. A Synthesis of Highway

Practice. NCHRP Synthesis 264. Washington, D.C.: Transportation Research Board, National

Research Council.

8 Aty, M. A. (2001). State-of-the-Art Report on: Roundabouts Design, Modelling, and Simulation.

Orlando, Florida: University of Central Florida.

9Alberta Transportation. (2010 and subsequently revised). Design Bulletin 68: Roundabout Design

Guidelines on Provincial Highways. Alberta Transportation.

Table I. Available High and Low Average Daily Traffic Volume Counts

Based on AADT

Year Bragg Creek* Cold Lake Pincher Creek Sylvan Lake Villeneuve

High Low High Low High Low High Low High Low

2002 8190 6870 2750 1250 3450 1280 6180 4550 5020 1330

2003 8280 6930 2000 1140 3680 1280 6060 4930 5400 1180

2004 8280 6830 1980 1100 3700 1280 6360 5020 5640 1200

2005 8170 6690 2090 1180 3720 1280 6800 5440 6120 1300

2006 8330 6610 2250 1400 3880 1330 7430 5950 6710 1420

2007 9350 6550 2610 1450 4060 1380 7250 6350 7300 1460

2008 9070 6350 2910 1530 5500 1470 7200 6200 6600 2080

2009 9110 6370 2910 1530 5500 1470 7330 5640 6560 2080

2010 9440 6600 2890 1530 5500 1470 7440 4780 6920 2120

2011 9300 6540 3010 1530 5500 1470 8040 4780 7160 2120

2012 9300 6480 3290 1550 5400 1460 9900 4930 6760 2120

2013 9480 6430 4010 2220 5440 1460 10610 5300 6550 2110

*Bragg Creek west leg has been excluded from comparison as it is a minor access only and therefore not an

accurate representation of traffic volumes

18

ParameterUnit Hwy 55 Cold Lake

King's St Fort

McMurray

Hwy 22 & Hwy 8

Bragg Creek

Highway 11 at

Sylvan LakeTown of Peace River

Town of Pincher

Creek

Hwy + Control Section 55:18/892:04(N)/892: 63:11:00 22:14/8:06 11A:06/20:02 744:04 6:04/507:02

Construction Cost $ 4,750,000.00 N/A $ 5,620,864.97 $ 3,041,368.84 $ 2,002,527.83 $ 1,421,377.90

AT Regional OfficeNorth Central Region -

Athabasca

Fort McMurray

Region

Southern Region -

Calgary

Central Region - Red

Deer

Peace Region - Peace

River

Southern Region -

Lethbridge

Consultant Clifton Associates Reid Crowther AECOM Al-Terra Stantec ISL Engineering

Inscribed circle dia. m 49 60-73 60 48.9 50 50

Central island dia. - ex.

apron or curbm 19 18.6 41 29.5 37.4 26

Apron material

100 mm impressed

pigmented concrete /

150 mm ACP / 450

mm GBC, 700 mm pit-

run gravel, 150 mm

topsoil

N/A200 mm ACP and 450

mm GBC

175 mm concrete

coloured and

impressed over 150

mm granular

Light red paving

stones

Red color, 150 mm

fibre reinforced

concrete class HPC,

GBC average depth

500 mm to match

existing structure

Curb type

Semi-mountable curb

(110 mm on outside,

75 mm on inside

island); 150 mm

barrier curb around

central island

Semi-mountable curbs

on splitter islands,

truck apron curbs

around central and

outside aprons; barrier

elsewhere

Semi-mountable curb

around apron, barrier

around central island

Semi-mountable

modified curb around

apron, barrier curb

around inside circle

with landscaping

Semi-mountable curb

inside a concrete

apron with brick work

inside the semi-

mountable curb in the

centre

Semi-mountable curb

and gutter on outside

lanes

Apron width in. curb m 7.5 4.7 4 3 1.5 5

Height of apron above

circulatory road75 mm at 1% N/A 3% slope 1% slope 100 mm 75 mm sloped at 3%

Roadway material

150 mm ACP / 450

mm GBC / 700 mm

granular fill (pit-run)

N/A200 mm ACP and 450

mm GBC

200 mm ACP Type

H1 / 400 mm GBC /

150 mm subgrade

100 mm ACP / 250

mm GBC

60 mm ACP, 170 mm

ACP, 200 mm GBC,

granular fill

Circulatory road width m 6.5 5 5 6.4-8.1 4.8 7

Circulatory road slope % 2% N/A 2% 1-2% 2% 2%

# of lanes 1 varies from 1-2 1 1 1 1

# of approaches 4 4 4 4 5 4

TABLE II. REQUIRED GEOMETRIC DATA